The complex that can show optical activity is:

trans- $\left[\mathrm{Fe}\left(\mathrm{NH}_{3}\right)_{2}(\mathrm{CN})_{4}\right]^{-}$

cis- $\left[\mathrm{Fe}\left(\mathrm{NH}_{3}\right)_{2}(\mathrm{CN})_{4}\right]^{-}$

cis- $\left[\mathrm{CrCl}_{2}(\mathrm{ox})_{2}\right]^{3-}(\mathrm{ox}=$ oxalate $)$

trans- $\left[\mathrm{Cr}\left(\mathrm{Cl}_{2}\right)(\mathrm{ox})_{2}\right]^{3-}$